1. Field of the Invention
The present invention relates to an apparatus for performing group control on a plurality of elevators which are operated for a plurality of floors and, more particularly, an improvement of a group management elevator system having a distributed control function.
2. Description of the Related Art
In recent years, in order to improve operation efficiency of a plurality of elevators installed parallel to each other and to offer better elevator services to passengers, the elevators are systematically controlled by a small computer such as a microcomputer to be quickly assigned to hall calls at respective floors. That is, when a hall call is made, an elevator car which allows optimum service is controlled to be selected and assigned to the hall call, and other elevator cars are controlled not to respond to this hall call.
In group control of this system, some advanced group control systems have a learning function. Interfloor traffic and average arrival time intervals between the halls can be managed in real time on the basis of measurements of cage-call registration data and passenger load data upon response to each hall call, as disclosed in, e.g., U.S. Pat. No. 4,760,896, "Apparatus for Performing Group Control on Elevators", patented to Yamaguchi on Aug. 2, 1988. The measurement data are processed by a computer in units of time zones to detect an elevator utilization demand of each building. Group control such as determination of an optimum car in response to a hall call, setting of a busy morning (opening) time zone, a lunchtime zone, and a busy evening (closing) time zone, setting of dispersed waiting zones of the elevator cars in non-busy hours, and setting of the number of halt elevator cars for energy saving.
A group control apparatus generally manages distributed control by a plurality of small computers. An elevator car unit control apparatus as a slave connected to the group control apparatus as a master is constituted by a small computer such as a microcomputer in a digital arrangement. High-speed information transmission is performed between the computer in the group control apparatus and the computer in the elevator car unit control apparatus via a serial transmission line or the like.
In the elevator system for performing group control, a ratio of control software utilized by the microcomputers to control hardware is high. Therefore, the overall system is complicated and digitized to perform high-speed information transmission between the computers.
Under these circumstances, a conventional group control apparatus is a centralized control system. In this centralized control system, the group control apparatus exchanges basic data with respective elevator car unit control apparatuses, and performs data processing in units of cars on the basis of the basic data.
When the scale of the group control elevator system is increased, i.e., when the numbers of floors and cars are increased, the computers in the group control apparatuses are overloaded. In this case, when the demand for hall calls is increased, the computer processing is affected by its capacity. For example, in a system having a reservation display function, the computer of the group control apparatus has a large load. A processing period running from the generation of a hall call to the time of an indicator-ON of an optimum car varies depending on the numbers of floors and elevator cars. The load on the computers in the total system is unbalanced. In addition, when a system-down occurs, the group control function fails at once. As a result, computer processing efficiency for the total system is poor.
Under the above circumstances, distributed control of control functions of an elevator system using multiple stations has been developed to aim at averaging of the load balance of control computers.
A system configuration of distributed control of the control functions is shown in FIG. 15A to 15C.
FIG. 15A shows a hierarchical system in which a group management slave controller for performing processing of each car unit is combined in a one-to-one correspondence with a unit controller for controlling a control function of the unit elevator. Each group management slave controller is connected in a slavemaster relationship to a group management master controller which is independently arranged to control the total system.
FIG. 15B shows a hierarchical system in which the function of the group management master controller of FIG. 15A is assigned to one of group management slave controllers for performing processing of elevator car units.
FIG. 15C shows a system in which the function of each unit controller and the function of the corresponding group controller are performed by one control computer.
In either system described above, processing of each elevator car unit has a one-to-one correspondence with the control computer. Load distribution is performed on the basis of the master control mechanism management. Therefore, the group management master function can be shifted between the slave controllers or systems.
However, the slave control function is not shifted. If a given slave controller fails, it is difficult to allow the remaining control computers to provide a cooperation function, i.e., an autonomous compensation function. For this reason, when a group management slave controller corresponding to a given unit controller fails, group control for the respective elevator is maintained except for the elevator car belonging to the failed group management slave controller. However, the failed elevator car is kept inactive or out of group control, thus degrading utilization efficiency.
In the systems shown in FIGS. 15A and 15B, in order to control n controllers, n (FIG. 15B) or (n+1) (FIG. 15A) computers are required. The control load is changed due to the number of floors of a building and/or the grades of the control systems, and fixed n or (n+1) distributed control systems are required. Cost performance is degraded against the purpose of load distribution. As a result, the flexibility and versatility of the system become poor.
In the system shown in FIG. 15C, all controllers are commonly arranged in the same computers as the unit controllers which must maintain absolute reliability as compared with the group control system. For this reason, a function of the unit controller having a higher priority is degraded by an influence of the group control system generally having a large control load. In addition, an elevator car unit corresponding to a control computer which failed due to a failure of the group control system also fails.
In the system of FIG. 15C, once a unit control system fails, the failure results in a decisive failure of the system. In addition, a unit control system fails upon a failure of the group control systems having an entirely different function from that of the unit control system, thus posing significant problems on reliability and safety. The group control system has limitations that its processing must be performed during interruption of processing of the unit control system having the higher priority. Therefore, the system in FIG. 15C has application limitations by the number of floors and/or the grades of the control systems.
In all the systems of FIGS. 15A, 15B and 15C, n computers (FIG. 15B) or (n+1) computers (FIG. 15A) are required, or no computer is required but the unit control function and the computer function are commonly provided (FIG. 15C). Although the distributed control systems are arranged to aim at load distribution, versatility of load distribution efficiency is limited by the number of floors and/or the grades of the control systems. That is, the above conventional systems are not satisfactory from the viewpoint of creation of a distributed control system having autonomous controllability/compensatability.
In a system for performing group control on elevators, control computers are used for group control and unit control. In order to average the loads of the respective control computers and perform highly efficient control, distributed control is proposed to distribute functions necessary for group control to a plurality of computers. Distributed control is advanced, and a one-to-one correspondence between elevator car unit processing and unit control is established. Therefore, the load can be distributed by the master control mechanism management base. Each unit control apparatus for controlling various operations of the elevator unit and each distributed control apparatus for performing distributed control for group control are separately provided in accordance with the processing capacity and unit control reliability which is of prime importance. These apparatuses are arranged in units of elevator car units. In order to control n elevators in the group, the load is changed by the number of floors and/or grades of the control systems. However, n distributed control systems are required to result in a wasteful system.
When one of the group control systems fails, the unit control system corresponding to the failed group control system cannot exchange data for group control. Therefore, this unit control system for the failed elevator car is considered out of control and removed from group control. Although group control of the total system is normally performed, overall utilization efficiency is degraded.
In a system wherein the unit control function and the group control function are assigned to each unit control computer in order to reduce the cost, when the group control system fails, the unit control system fails accordingly. Therefore, reliability of unit control is degraded.